LAWRENCEVILLE -- A former Lilburn psychotherapist entered a surprise guilty plea this week to sexual assault charges involving a patient, costing him two years in prison and his professional license.

Cliff Tillery, 46, pleaded guilty in Gwinnett Superior Court on Monday to two counts of sexual assault by a practitioner of psychotherapy, just as jury selection in a retrial of the case was scheduled to begin, said Assistant District Attorney Jennifer Taylor.

Tillery will serve eight years, probation following his prison stint, said Taylor.

"I'm very pleased that he finally admitted that what he did to the victim was wrong," Taylor said.

Tillery, 46, admitted to coercing the victim -- a Gwinnett preschool teacher with a history of alcohol and sexual abuse -- into sexual activity more than 20 times at his Norcross office in 2007. She paid $85 per hour for most sessions.

Tillery was originally tried in March, when a judge declared a mistrial after jurors couldn't reach a unanimous decision after deliberating for nearly two days.

The charges carried a possible 60-year prison term, Taylor said.

Tillery's defense attorney, Dylan Wilbanks, did not return a call seeking comment Wednesday. Taylor said she'd been contacted by the defense Friday with word that Tillery was considering a plea deal.

Special conditions of Tillery's sentencing will require him to register as a sex offender, avoid the victim and her family, and undergo psychosexual evaluations, Taylor said.

Tillery surrendered his professional license Monday and won't be allowed to treat patients in any capacity while on probation, she said.

Tillery had spent more than 20 years in the field before his July 2008 arrest. He worked with drug addicts, sex addicts and alcoholics.

Both parties were married with children at the time.

The 32-year-old victim told the Daily Post on Wednesday she felt the sentencing was "a little lenient" but sends "a huge message for anybody in a position of power." She feels that Tillery brainwashed her into acts she wouldn't have considered otherwise.

The Daily Post does not identify victims of sex abuse.

"I think he knew he couldn't win at trial," she said of Tillery.

As for going forward, she said, "I will continue to advocate for victims. I feel like I have a whole new purpose now."

Prior to sentencing, Tillery apologized to the victim and her family, Taylor said.